The present invention relates generally to automatic sewing apparatus, and in particular to automatic sewing apparatus having means for preventing damage to the apparatus during certain modes of its operation, or due to improper operation.
In the mass production of clothing, shoes, and the like, it is common to use automatic sewing apparatus which automatically move a workpiece in a predetermined pattern relative to a sewing head for stitching. The workpiece is supported on a movable support carriage, the movement of which may be controlled in a predetermined manner by a numerical or direct digital control system. Because the workpiece materials used for clothing or shoes are rather flaccid, e.g. cloth or leather, the workpiece is generally held within a pallet, such as disclosed, for example, in U.S. Pat. No. 3,988,993 to Brophy, issued Nov. 2, 1976, comprising plates which are assembled in a sandwich-type arrangement. Aligned openings or cut-outs are provided in the plates adjacent to areas of the workpiece to be stitched to permit access to the workpiece by the presser foot and the needle of the sewing head. The pallet is mounted on the support carriage, and the control system automatically moves the support carriage to position a cut-out below the sewing head, lowers the presser foot to engage the workpiece within the cut-out, and moves the carriage in a predetermined pattern so that the workpiece is stitched along a path within the cut-out. Upon completion of a stitching operation, the control system automatically raises the presser foot, moves the support carriage to position the next cut-out below the sewing head, and performs another stitching operation.
If the thread breaks or the bobbin runs out during stitching, it is necessary to backstitch over the holes in the material that do not have thread. This is accomplished by backtracking along the previously stitched path. During backstitching, however, the presser foot may not be automatically raised when it comes to the edge of a cut-out. Accordingly, the presser foot may strike the pallet, causing damage to the presser foot or the presser foot suspension bar, necessitating down time of the apparatus and costly maintenance to replace the damaged parts. Moreover, if the pallet is not properly aligned with respect to the support carriage prior to beginning a sewing operation, the cut-outs in the pallet will not be properly positioned with respect to the sewing head. This may allow the presser foot or the needle to strike the pallet, causing damage to the sewing head.